Description: The compact Elecraft KXPA100 amplifier is intended for use
with all QRP transceivers. It's particularly well suited to
the Elecraft KX3 transceiver. The amp covers the 160-6 meter
bands, including the WARC bands, and is rated at 100 W
nominal power output (+/- 1 dB). A companion internal
automatic antenna tuner (ATU), the KXAT100, is also
available.

The AMP was bought for have duty using in contests. It work excellent with my transceiver SunSDR2Pro in SO2RX mode. The general excellence is extremely fast switching bands/antennas/ATU-memories. All switches doing by the CAT-commands via rs232 port (usb<=>rs232). When it used with new TCI interface SunSDR2Pro, all switchings performed in few milliseconds before begin transmitting. As result, extremely durable pack for SO2RX Low Power contesting.

Elecraft’s KX3 has been my one and only rig for the past five years. Conditions have not been so good of late, and this is expected to persist for some time. Several QSOs cut short due to the strength of my signal during a poor sunspot day, and QST’s recent review, convinced me of the need for an occasional rise above the 15 watt level I most often run at, and so I purchased a factory-assembled KXPA100 100 watt linear amplifier including the optional KXAT100 antenna tuner.

I love the design of the KXPA100. ELEgantly CRAFTed and coordinated with the PX3 and KX3. Operationally, the amplifier integrates seamlessly with the KX3 and can be totally controlled from the KX3. Signal reports have been terrific and it’s nice knowing the power’s there when I need it.

The specs convinced me to get a new power supply to feed my KXPA100, KX3 and PX3. I went with the Powerwerx 30 amp SS-30DV that Elecraft recommends (and resells). Its internal and external design are such that it could be called a KXPS. Visually, it matches the KX3 line. I like that it has two Powerpole connectors on the front, and ¼-inch connectors on the rear.

KX3 owners, be cognizant that you need to order the KX3 to KXPA100 adapter cable set separately. This is apparently done because the amplifier is also sold for other rigs besides the KX3.
Bob - W2TAC

I originally used the amp for my KX3 and now for my recently acauired KX2. Works well with these Elecraft radios and is of the quality expected. I had mine factory built and aligned. I like the auto attenuation when I apply more than the radio is designed for. I don't really pay much attention to it as with the auto tuner, there is nothing much to do but pay a little attention on occasion to the front panel controls. I use the amp only when needed and I am not heard QRP. The product is solid and makes great power for both of the portable radios in the shack. I get good signal reports, both audio and cw.

This is an update on my earlier review. I am enjoying my KXPA-100 on all modes in conjunction with my Apache Labs ANAN-10E transceiver. The ANAN-10E employs "adaptive pre-distortion" to reduce IMD. Using adaptive pre-distortion, the 3rd order intermodulation products (2-tone test)... with the KXPA-100 producing 100W peak power output... are more than 50dB below the two principal tones.

However, without the use of adaptive pre-distortion, the 3rd order intermodulation products (2-tone test)... with the KXPA-100 producing 100W peak output power... are less than 20dB below the two principal tones. With the KXPA-100 bypassed, and with the ANAN-10E producing 5W peak output power, the 3rd order intermodulation products (2-tone test) are more than 40dB below the two principal tones.

Therefore, with my KXPA-100, the 3rd order IMD (without adaptive pre-distortion), with 100W peak output, is less than 20dB below the principal modulation components.

I bought this amp as a kit last year. It now works well and delivers the rated power. However when I first put it on the air, there was 10-20dB RX noise going to the transceiver on all bands, The entire unit was replaced by Elecraft, but I had to pay the high cost of return from Australia to the US, for a fault that should have been picked up by quality control, and the cause of which was never explained. The support people were very helpful, but this was not a good experience following on from the a major mike input problem that I copped on my KX3 some years ago, when there was a run of faulty control panel boards.

This is a good little amp and it works pretty well. I am happy with it as I can get 110 watts out of it as measured on an external meter but I typically run it at about 80 watts. I rate it a 4 because there a couple of niggles everyone needs to know about. None are showstoppers but hey it is a pretty high priced amp.

The mechanical design is well a brick. It looks like the mirage 2m amps. I think they could have done better.

While the build from kit was easy, it is not easy to get back into the kit if needed. In fact you pretty much have to take out 32 little screws to get it open at all. I worked for a company that designed computers and servers, there could be no externally exposed screws and it had to open with one hidden knob, so it can be done - those guys were mechanical engineering geniuses!

The amp is designed to talk to the KX3 and computer through a serial interface, this means you daisy chain the KX3 to the amp to the computer. I have found this can cause comm problems with rig control and software programs.

The ATU on the amp is not as good as the internal ATU in the KX3. I find that the ATU in the amp stops .1 or .2 SWR units higher than the KX3 ATU. I've also noticed that in some instances the tuned SWR is lower than the operational SWR. I am not sure what is going on with that but I am working with Elecraft on it and am confident we will come up with an answer.

I've also noticed that when I stop transmitting, there is a significant delay in the response of the front panel LEDs. The 25W LED and the SWR LEDs will stay on for 1.5 to 2 seconds after key up.

Finally, when the ATU tunes, the firmware puts the amp in bypass mode so it is just the KX3 working with the ATU to tune. After tuning, there is a about a 1.5 second delay before the amp switches back in. So if you tune up and then try to transmit too quickly, you will be transmitting without the PA and at the lower tuning power.

Maybe I just have a problem with my ATU and I will continue to work with Elecraft to figure it out. I think the AMP is fine and does what it is suppose to do, but I may have an issue with my ATU.

Well worth the cost. Easy to build, easy to use, and very portable. It is a great tool for those that want to run a low power, low current draw qrp rig and for poor band conditions or emergencies have the extra 100 watts of power. With the cables it is all automatic with the KX3. Just turn on your little qrp radio and use it like any other 100 watt radio. It's a good feeling to have the extra power if needed. Like the other Elecraft equipment it is better than I expected. I haven't had the amp a long time but I can say it works very well. I look forward to using the KXPA 100 for traveling and camping in the mountains of Colorado.

I received my kit version, Ser. No. <300, several weeks ago. I have had a KX3, with most of the fixings, since early July 2012. I think the KX3 is about everything I have ever wanted in a radio. As we know, the receiver is amazing, so the real "problem" has been to transmit with enough power to increase the chance that station you could hear will hear you. If you have only wire antennas, as I do, this power addition is very useful.

Construction: I dragged the construction out to about 2 hours, by photographing every single step, and savored every turn of every screw. This thing is so simple, a lawyer can do it.

Operation: As others have noted, I now get quick replies, even in pile ups. Voice quality reports are positive, which is what I got with the barefoot KX3. It is important to adjust the TX equalizer to make your voice work at distance. I have found that PSK 31 and RTTY signals are easily read by others. As with the barefoot, CW is a dream. I have not put this on a spectrum analyzer ['cause I don't have one], but performance suggests the signal is quite clean.

Operation with the KX3 using the optional connector cable set is seamless, and the rig simply becomes a 100 watt Elecraft transceiver, with all that means.

Setting changes are extremely easy, using the same buttons and knobs used for barefoot KX3 operations.

Follow the relatively simple directions in the manual to avoid problems. I have made a couple of mistakes, but the amp tells the KX3 and it promptly tells me I am an idiot.

Computer interface with both the KXPA100 utility and the regular KX3 utility has been flawless. With the amp, I can now reasonably participate in SSB contests. In CW contests, where N1MM allows me to operate mostly from the keyboard [using a simple homebrew interface], I can now move out of the QRP class and hope to make many more contacts.

My generic switching power supply suggests that I am drawing well below the nominal 20 amps in the specs. I have had no problems in this regard. Because of size and efficiency, this is a rig that I can expect to use during ARRL Field Day from the field with marginal power demands [even batteries.]

ATU: The ATU is quite sensitive to antenna conditions, and is consistent with what my analyzer says those conditions are. It matches everything I have tried quickly. Follow the instructions, especially regarding the "programming" into memory many spots in each band. This makes shifts to the next band as fast as you will see with any other ATU. It surpasses my excellent LDG Z-11Pro on the same antennas. Once tuned, it stays tuned.

Summary: The KX3 is still a wonderful QRP radio, and I continue to enjoy using it at 5 watts. The easy settings, quick and steady ATU, and plentiful power provided seamlessly by this amp enable me to make contact with almost everyone I can hear [within the reasonable limits of my wire antennas.] I STRONGLY recommend this to anyone who has a KX3 and wants to make it reach out to all of those folks [and make life easier for them trying to listen to you....]

I recieved my assembled amp SN 484 on January 8, 2014.
The packaging was superb and the instructions are very easy. In a matter of minutes I had it hooked up to my KX3 and after a few minor menu settings had it on air. I ordered it with the internal ATU and it tuned up my Matchbox Endfed antenna quickly. I was on the air with excellent reports from miles away. Clean!

I absolutly love my KX3 and having the KXPA100 in the shack gives me the best of both worlds - QRP portable and up to 100 watts in the shack!

Ordered as a kit, assembly is very easy, even if only a beginner, no soldering required.

Highlights:

- The KXPA seamlessly integrates with the KX3, even computer control/info is passed through with only one cable necessary.
- Amp has a small footprint with a large heatsink, completely silent and no fan necessary.
- KXPA amp software is available for Linux/Mac/Windoze.
- Excellent printed manual/assembly instructions.
- Easy to adapt to other Rigs
- Price is a value considering the flagship device/options/support/performance/continuous improvement you receive.